Because of concern about the safety of U. S. licensed immune globulins (IG), we continued to monitor HCV RNA levels in FDA released lots by our PCR method (see previous annual report). Among 25 lots of intramuscular IG which include some specific IG, 14 of 23 lots prepared from Source Plasma (SP) were positive while 2 lots from recovered plasma (RP) were negative. HCV RNA ranged from 30 to 500 PCR U/g IgG. HCV RNA was also detected in 11 of 32 lots of intravenous IG prepared from SP by 6 manufacturers. All positive lots were derived from the same manufacturer; 11 of the 14 lots were positive with levels ranging from 2 to 250 PCR U/g IgG. However, 6 lots prepared from RP by the same process and by the same manufacturer were negative. An additional 6 lots prepared from RP by 2 other manufacturers were also negative. This may be attributed to the lower anti-HCV reactive rate, and hence, the lower viral load in RP. The effect of plasma screening by anti-HCV on the level of HCV RNA in IG remains unknown since products manufactured solely from screened plasma are not yet available. HCV RNA detected in IG appeared not to exist as a free (not encapsulated) single-stranded RNA since it was not digestible by ribonuclease A (40 units/ml at 37 degrees C for 3 h). In addition, it was not present as a fragmented RNA since downstream sequences, i.e., the putative NS3 and NS5 coding regions of the HCV genome, were also detected when primers from those two regions in addition to those from the 5' non-coding region were used for PCR. The buoyant density (bd) of HCV in a PCR positive IG was determined by sucrose gradient ultracentrifugation to be 1.16 g/cm3, similar to that determined in a single donor plasma sample, i.e., 1.15 g/cm3. When a plasma sample was treated with 25% ETOH (22 h at 4 degrees C), the bd of HCV was 1.20, whereas treatment with 0.1% NP40 resulted in a bd of 1.28. Hence, ethanol may alter the viral envelope during plasma fractionation, but not to as great an extent as does NP40, which may expose the core of HCV. The nature and significance of HCV RNA detected in immune globulins requires further elucidation.